The present invention relates to 2-methyl-4-pentenoic acid and C.sub.2 -C.sub.6 alkyl esters thereof and novel compositions and processes using such 2-methyl-4-pentenoic acid and esters to alter the flavor of foodstuffs, chewing gums and medicinal products.
There has been considerable work performed related to substances which can be used to impart (or enhance) flavors to (or in) various types of foodstuffs, chewing gums and medicinal products. These substances are used to diminish the use of natural materials, some of which may be in short supply and to provide more uniform properties in the finished product. Sweet, fruity, strawberry, winey-cognac, cooked strawberry jam, pineapple-like, pear, green and apple-like aromas as well as tastes are particularly desirable for manay uses in foodstuff flavors.
U.S. Pat. No. 3,499,769 issued on Mar. 10, 1970 discloses processes for imparting a fresh fruity flavor (particularly strawberry flavor) to foods by adding a small amount of 2-methyl-2-pentenoic acid to the foodstuff. In U.S. Pat. No. 3,499,769 it is emphasized that the basic nuance imparted by the 2-methyl-2-pentenoic acid is a "berry" flavor.
Quite unexpectedly, the 2-methyl-4-pentenoic acid and esters thereof of the instant invention have properties different in kind from the 2-methyl-2-pentenoic acid of U.S. Pat. No. 3,499,769 which is only fruity and strawberry-like and does not have the sweet, fruity, winey-cognac, pineapple-like, pear, green and apple-like aroma and taste qualities of the 2-methyl-4-pentenoic acid and esters thereof of the instant invention.
Arctander, "Perfume and Flavor Chemicals", 1969 discloses the use in perfume compositions and flavors of 4-pentenoic acid, thus:
" . . . only rarely used in perfume compositions mainly on fruity bases and certain artificial essential oils. PA1 It finds use in flavors on account of its sour-caramellic taste, pleasant at levels below 10 ppm, and including an almost sweet aftertaste. Higher concentrations have acrid taste and repulsively acid odor, pungent and irritating. PA1 Traces, equivalent to 1 to 5 ppm, are used in imitation butter flavor and in various fruit flavor complexes, e.g., apple, pinapple, apricot and strawberry." PA1 "Spicy-rooty, sweet-sour herbaceous odor of moderate tenacity." PA1 a. First reacting 1,1,1-triethoxypropane with 2-propenol-1 in the presence of a phosphoric acid catalyst to form ethyl-2-methyl-4-pentenoate. The reaction temperature range is 100.degree.-225.degree.C with a range of 140.degree.-180.degree.C being preferred. The mole ratio of reactants preferred is 1:1, with a large excess of 2-propenol-1 undesirable and a large excess of triethoxypropane being uneconomical. The reaction time is inversely dependent upon the temperature of reaction. Thus, for example, where the temperature range of reaction is 165.degree.-185.degree.C, the reaction time is approximately three (3) hours. As stated, supra, the reaction product, ethyl-2-methyl-4-pentenoate may be used as is, or it may further be reacted as in step (b) or (c), set forth infra; but in any event, the reaction product is "worked-up" by first neutralizing the acid catalyst, the phosphoric acid, using base (e.g., sodium bicarbonate) and then fractionally distilling the reaction product. PA1 b. If desired, the resulting ethyl-2-methyl-4-pentenoate may be converted into 1-methyl-4-pentenoic acid by the standard saponification and acidification reactions. The saponification is preferably caried out using strong aqueous base, e.g., 50% aqueous sodium hydroxide or 50% aqueous potassium hydroxide admixed with methanol. After acidification of the resulting salt of 2-methyl-4-pentenoic acid (e.g., the sodium or potassium salt) using mineral acid (e.g., 6 molar aqueous hydrochloric acid) the 2-methyl-4-pentenoic acid is extracted from the aqueous phase using an organic solvent such as toluene. The organic solvent is then stripped from the acid and the acid is fractionally distilled. The resulting acid may be used as such, or it may, if desired be esterified with a C.sub.3 -C.sub.6 alkanol to form an ester of 2-methyl-4-pentenoic acid. PA1 c. If desired, the ethyl-2-methyl-4-pentenoate produced as set forth in (a), supra, may be converted into another ester, a C.sub.3 -, C.sub.4 -, C.sub.5 - or C.sub.6 - ester of 2-methyl-4-pentenoic acid, by reaction with a C.sub.3 -, C.sub.4 -, C.sub.5 - or C.sub.6 - alkanol in the presence of a protonic acid catalyst at a temperature in the range of 100.degree.-170.degree.C. The preferable temperature depends upon the particular alkanol used; e.g., about 110.degree.C in the case of isobutyl alcohol; and 140.degree.-150.degree.C in the case of n-hexanol. The preferred catalyst is paratoluene sulfonic acid. PA1 a. First reacting a 1,1,1,-trialkoxy propane (such as 1,1,1-triethoxy propane, or 1,1,1-trihexyloxy propane) with 2-propynol-1 in the presence of a propionic acid catalyst thereby forming an alkyl-2-methyl-3,4-pentadienoate. The reaction temperature range is 120.degree.-180.degree.C with a range of 145.degree.-150.degree.C being preferred. The mole ratios of reactants preferred is 1:1 with a slight excess of either reactant permissible. A large excess of 2-propynol-1 is undesirable, and a large excess of the trialkoxy propane is uneconomical. The percentage of propionic acid catalyst may vary from 1 up to 3%, but a 2% concentration of catalyst is preferred. Since the reaction temperature is in the range of 120.degree.-180.degree.C higher pressures of reaction are required for the carrying out of the reaction, and, accordingly, pressures of from 30 up to 100 psig are used. The reaction time is inversely dependent on the temperature of reaction. Thus, for example, where the temperature range of reaction is 150.degree.- 160.degree.C, the reaction time is approximately 3 hours. The reaction time period varies between 2 and 6 hours, and a reaction time of 3-4 hours is preferred. The reaction product, the alkyl-2-methyl-3,4-pentadienoate, is then worked-up and this work-up operation is performed by first, if necessary, washing out the excesss trialkyl orthopropionate reactant by washing with a dilute (e.g., 5%) hydrochloric acid solution. The acid is then neutralized by use of a sodium bicarbonate wash, and the reaction mass is then fractionally distilled. PA1 b. The resulting alkyl-2-methyl-3,4-pentadienoate is then reacted with hydrogen in the presence of a palladium-on-carbon catalyst or a "Lindlar" catalyst (palladium-on-calcium carbonate). The percentage of palladium on carbon or on calcium carbonate varies from about 2% up to about 7% with a percentage of palladium-on-carbon or on calcium carbonate being preferred to be about 5%. The temperature of reaction for this hydrogenation may vary from about 10.degree.C up to about 50.degree.C with a preferred reaction temperaturea of 25.degree.-35.degree.C. Since the reaction is exothermic, it is usually necessary to provide external cooling to the reaction mass during the course of the reaction. The pressure of hydrogen over the reaction mass may vary from about 5 psig up to about 50 psig, with the most preferred pressure being 20 psig. It has been found that pressures above 20 psig give rise to larger amounts of undesired side products. The hydrogenation reaction may be carried out in the presence of or in the absence of a solvent. When a solvent is used, it is required that it be an inert (non-reactive) solvent such as isopropyl alcohol, hexane or ethanol, with the alkyl moiety of the alcohol solvent being the same as the alkyl moiety of the alkoxy group of the ester being hydrogenated. If a solvent is used, it is preferred that the mole ratio of solvent:pentadienoate ester be approximately 1:1. The percentage of catalyst in the reaction mass may vary from 0.125% up to about 2.0% with a percentage of catalyst of about 0.25% being preferred. When using a Lindlar catalyst, the hydrogenation reaction produces a mixture of alkyl-2-methyl-cis-3-pentenoate and alkyl-2-methyl-4-pentenoate in the ratio of from about 6:4 up to about 7:3. As a result, the desired alkyl-2-methyl-4-pentenoate for use in the instant invention may, if desired, be enriched with respect to the alkyl-2-methyl-cis-3-pentenoate by means of fractional distillation or the mixture resulting may be used as such for its organoleptic properties as a flavor adjuvant or enhancer for use in foodstuffs, medicinal products or chewing gum. Where the catalyst used is palladium-on-carbon rather than a Lindlar catalyst (palladium on-calcium carbonate), a mixture of alkyl-2-methyl-cis-3-pentenoate, alkyl-2-methyl-4-pentenoate and alkyl-2-methyl-pentanoate is formed which may be used as such for its organoleptic properties as a flavor adjuvant or enhancer for foodstuffs, chewing gum and medicinal products or which may be separated as by means of fractional distillation. In any event, at the end of the hydrogenation reaction, the reaction mass is filtered in order to separate catalyst from liquid phase desired product, and the filtrate is distilled using a fractional distillation column operated under vacuum. PA1 c. If desired, the resulting alkyl-2-methyl-4-pentenoate and other esters which have not been separated therefrom after the hydrogenation reaction may be converted into 2-methyl-4-pentenoic acid and other acids by means of standard saponification and acidification reactions. The saponification is preferably carried out using strong aqueous base, e.g., 50% aqueous sodium hydroxide or 50% aqueous potassium hydroxide admixed with methanol. After acidification of the resulting salt of 2-methyl-4-pentenoic acid (e.g., the sodium or potassium salt) using mineral acid), the 2-methyl-4-pentenoic acid is extracted from the aqueous phase using an organic solvent such as diethyl ether. The organic solvent is then stripped from the acid, and the acid is fractionally distilled. The resulting acid may be used as such or it may, if desired, be esterified with a C.sub.3 -C.sub.6 alkanol to form an ester of 2-methyl-4-pentenoic acid. PA1 d. If desired, the mixture of esters including the alkyl-2-methyl-4-pentenoate ester produced as set forth in (b) supra, may be converted into other esters, such as a C.sub.3, C.sub.4, C.sub.5 or C.sub.6 ester of 2-methyl-4-pentenoic acid by reaction with a C.sub.3, C.sub.4, C.sub.5 or C.sub.6 alkanol in the presence of a protonic acid catalyst at a temperature in the range of 100.degree.-170.degree.C. The preferred temperature depends upon the particular alkanol used; e.g., about 110.degree.C in the case of isobutyl alcohol; and 140.degree.-150.degree.C in the case of n-hexanol. The preferred catalyst is paratoluene sulfonic acid. PA1 p-Hydroxybenzylacetone; PA1 Geraniol; PA1 Maltol; PA1 Ethyl methyl phenyl glycidate; PA1 Benzyl acetate; PA1 Vanillin; PA1 Methyl cinnamate; PA1 Ethyl pelargonate; PA1 Methyl anthranilate; PA1 Isoamyl acetate; PA1 Alpha ionone; PA1 Ethyl butyrate; PA1 Gamma-undecalactone; PA1 Naphthyl ethyl ether; PA1 Diacetyl; PA1 Ethyl acetate; PA1 Anethole; PA1 Isoamyl butyrate; PA1 Cis-3-hexenol-1; PA1 2-Methyl-2-pentenoic acid; PA1 Elemecine (4 -allyl-1,2,6-trimethoxy benzene); PA1 Isoelemecine (4-propenyl-1,2,6-trimethoxy benzene)
at Volume II, No. 2452. Artctander also discloses the use of trans-2-methyl-2-butenoic acid (tiglic acid) at Vol. II, No. 2949 in perfumery:
and the use of cis-2-methyl-2-butenoic acid (angelic acid) and alkyl esters thereof in perfumes and flavors at Vol. I, No. 238.
The alkenoic acids and esters thereof of the prior art are considered to be different in kind from the 2-methyl-4-pentenoic acid and C.sub.2 -C.sub.6 alkyl esters thereof of the instant invention insofar as their organoleptic properties are concerned.
Rossi and Ingrosse, Chem.Abstr. 69, 95851(g) (Abstract of Gazz.Chim.Ital. 98(7), 866-83 (1968) ) discloses the preparation of 2-methyl-4-pentenoic acid by reacting 3-chlor-propene-1 with 1,1-dicarboethoxyethane.
De Moura Campos and de Amarat, Chem.Abstr. 63: 4159(e) (Abstract of J.Arch.Pharm. 298(2), 92-100 (1965) discloses the preparation of 2-methyl-4-pentenoic acid by the following reaction sequence: ##SPC1##
Trace and Gurante, Chem.Abstr. 55:14324(i) (Abstract of Rend.Inst.Lombardo Sci. Pt.I, Classe Sci. Mat. e Nat., 94A, 309-330 (1960) discloses a process for preparing 2-methyl-4-pentenoic acid by reacting 2-cyclopropyl-propionic acid with HBr.
Adler and Brachel Chem.Abstr. 57: 2042(d) (Abstract of Ann. 651, 141-53 (1962) sets forth a process for giving 12% yields of methyl-2-methyl-4-pentenoate by means of the following reaction: ##SPC2##
These processes as well as other processes of the prior art have not been found to have lower commercial feasibility in view of the complexity and/or cost of carrying out the particular reaction involved; as distinguished from the novel process of our invention.